title: Glucocorticoid effects in the human placenta: evidence that dexamethasone-mediated inhibition of fibronectin expression in cytotrophoblasts involves a protein intermediate.
abstract: Oncofetal fibronectin is an extracellular matrix protein that is suggested to play an important role in regulating adherence at uterine-placental interfaces. The purpose of the present study was to elucidate a mechanism through which glucocorticoids (GCs) inhibit the synthesis of FN in human placenta as part of their matrix-suppressive action near parturition. We observed that treatment of cytotrophoblasts isolated from human term placentas for 48 h with 10(-7) mol/L dexamethasone (DEX) down-regulated levels of FN expression to 13-19% of control levels in immunoprecipitation, Northern blotting, and enzyme-linked immunosorbent assay experiments. Conversely, GC treatment increased FN expression in placental fibroblasts to 164-310% of control levels in Northern blotting and enzyme-linked immunosorbent assay procedures, suggesting that GC-mediated suppression of FN expression is specific to cytotrophoblasts. Results indicated that the DEX-mediated suppression of FN expression in cytotrophoblasts was not mediated through changes in the stability of FN messenger ribonucleic acid (mRNA). Run-on transcription assays using isolated nuclei suggested that GC treatment did not markedly affect transcription of the FN gene in cytotrophoblasts. To test whether the GC-mediated suppression of FN expression was mediated through a protein intermediate, levels of FN mRNA were examined by Northern blotting in cells treated for 48 h with and without 10(-7) mol/L DEX and cycloheximide (CHX; 125 ng/mL). We observed that CHX treatment increased FN expression in DEX-treated cells to 91% of control values. We noted that whereas the presence of 100-300 ng/mL CHX reversed the DEX-mediated inhibition of FN mRNA expression in cytotrophoblasts, it did not alter the overall rates of protein synthesis in DEX-treated and control cells. These data suggest that suppression of FN mRNA expression by GC in cytotrophoblasts requires de novo protein synthesis and is mediated through a short lived intermediate, the synthesis of which is inhibited at low concentrations of CHX. Thus, GC-induced protein intermediates may influence uterine-placental adherence by modulating levels of oncofetal FN at sites of uterine-placental contact.
authors.affiliation: New York University Medical Center, New York 10016, USA.
authors.forename: D Y
authors.initials: DY
authors.lastname: Yoon
authors.forename: Y
authors.initials: Y
authors.lastname: Ma
authors.forename: G
authors.initials: G
authors.lastname: Krikun
authors.forename: C J
authors.initials: CJ
authors.lastname: Lockwood
authors.forename: L
authors.initials: L
authors.lastname: LaChapelle
authors.forename: S
authors.initials: S
authors.lastname: Guller
mesh_terms: D015152:Blotting, Northern; D002478:Cells, Cultured; D003513:Cycloheximide / Q000494:pharmacology; D003907:Dexamethasone / Q000494:pharmacology*; D004797:Enzyme-Linked Immunosorbent Assay; D005260:Female; D005347:Fibroblasts / Q000378:metabolism; D005353:Fibronectins / Q000096:biosynthesis / Q000235:genetics*; D015870:Gene Expression / Q000187:drug effects*; D006801:Humans; D007163:Immunosorbent Techniques; D007700:Kinetics; D011247:Pregnancy; D011500:Protein Synthesis Inhibitors / Q000494:pharmacology; D012333:RNA, Messenger / Q000378:metabolism; D014158:Transcription, Genetic / Q000187:drug effects; D014327:Trophoblasts / Q000187:drug effects* / Q000378:metabolism*
chemical_list: D005353:Fibronectins; D011500:Protein Synthesis Inhibitors; D012333:RNA, Messenger; D003907:Dexamethasone; D003513:Cycloheximide